1. Field of the Invention
The present invention relates to a magnetic head in a magnetic read/write device characterized by an arrangement wherein the magnetic head is not susceptible of disturbance from magnetic field.
2. Description of the Prior Art
For convenience of explanation, a description here will be made of an example of a read/write magnetic head of a floppy disc.
In magnetic read/write devices the floppy discs an increase in storage capacity and miniaturization of the device have been particularly required recently.
Processes for increasing the storage capacity considered possible include increasing the recording density of the floppy disc or increasing the track density. In either case, however, difficulties are involved in that the reading output voltage of the magnetic head is low so as to deteriorate the ratio of signal to noise (S/N ratio).
On the other hand, if the miniaturization of devices is further realized in the future, it can be considered that there will be an increased possibility that the distance from the magnetic head to other noise sources, for example, a relay, transformer, reactor CRT, PWB, etc. is small, in which case the S/N ratio is also deteriorated.
It can be said therefore that the increase in storage capacity and the miniaturization of the device will depend on how disturbance from noise components can be decreased.
A magnetic shield is effectively used to prevent the disturbance from magnetic noise applied to the magnetic head.
This magnetic shield, as is well known, can provide a maximum effect by covering the whole surface of an object to be shielded by a ferromagnetic material. However, in case of a magnetic head, it is essentially impossible to cover a surface in contact with a floppy disc. Thus, it is necessary to find a method of providing maximum shielding under the condition that the surface in contact with the floppy disc cannot be covered.
Magnetic shielding methods for the magnetic head heretofore carried out are as shown in FIGS. 1 and 2.
In the case of FIG. 1, a head piece 1 comprising a core and a coil is surrounded by a permalloy ring 2. In the case of FIG. 2, a channel-like permalloy 3 covers a lower portion (the side opposite the surface in contact with the disc) of the head piece 1.
The above-described conventional methods have a disadvantage in that the shield effect with respect to the magnetic field noise of frequencies in excess of several 10 KHz is small. According to actual measurements, the shield effect is approximately 4-6 dB in the low frequency magnetic field and is approximately 1-2 dB in the high frequency magnetic field.
As the result of various experiments and studies, the present inventors have found and provide a method for obtaining a shield effect with respect to the magnetic field noise have a relatively high frequency.